<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <script>
        // 定义变量
        /*
        var iNum = 12;
        var sTr = "hahaha";
        var bBool = true;
        */
        var iNum01 = 12, sTr = "haha", bBool = true;
        // 变量声明但是没有初始化, 它的值和类型都是 undefined
        var iNum02;
        alert(iNum01);
        alert(sTr);
        alert(bBool);
        alert(iNum02);


    </script>
</head>
<body>

</body>
</html>